Method for Producing Recycled Polyethylene with Virgin-Like Optical Properties

ABSTRACT

A method for purifying a contaminated reclaimed polyethylene is provided. The method comprises obtaining the contaminated reclaimed polyethylene, extracting it with a solvent to produce an extracted contaminated reclaimed polyethylene, and then dissolving it in the solvent to produce a first suspension comprising dissolved polyethylene and suspended contaminants. The first suspension is settled to produce a second suspension comprising dissolved polyethylene and suspended remaining contaminants, and the second suspension is purified by contacting it with solid media to produce a third suspension comprising purer polyethylene. Finally, the purer polyethylene is separated from the third suspension and it has virgin-like optical properties.

FIELD OF THE INVENTION

The present invention generally relates to a method for purifyingcontaminated reclaimed polyethylene (crPE) through the use of apressurized solvent, and extraction and dissolution steps. Morespecifically, this invention relates to a method for purifying crPE,such as post-consumer recycled PE (PCR PE) and post-industrial recycledPE (PIR PE), to produce recycled PE with virgin-like optical properties(vlPE). Any of the various grades of contaminated reclaimedpolyethylene, such as high-density polyethylene (crHDPE), low-densitypolyethylene (crLDPE), linear low-density polyethylene (crLLDPE), andtheir mixtures, can be used as feedstocks in the present invention toproduce vlPE.

BACKGROUND OF THE INVENTION

Polymers, especially synthetic plastics, are ubiquitous in daily lifedue to their relatively low production costs and good balance ofmaterial properties. Synthetic plastics are used in a wide variety ofapplications, such as packaging, automotive components, medical devices,and consumer goods. To meet the high demand of these applications, tensof millions of tons of synthetic plastics are produced globally on anannual basis. The overwhelming majority of synthetic plastics areproduced from increasingly scarce fossil sources, such as petroleum andnatural gas. Additionally, the manufacturing of synthetic plastics fromfossil sources consumes a lot of energy and produces CO₂ as aby-product.

The ubiquitous use of synthetic plastics has consequently resulted inmillions of tons of plastic waste being generated every year. While themajority of plastic waste is landfilled via municipal solid wasteprograms (about 79% globally) or incinerated for energy recovery (about12% globally), a significant portion of plastic waste is found in theenvironment as litter, which is unsightly and potentially harmful toecosystems. Plastic waste is often washed into river systems andultimately out to sea.

Plastics recycling has emerged as one solution to mitigate the issuesassociated with the wide-spread usage of plastics, their end-of-life,and their leakage to the environment. Recovering and re-using plasticsdiverts waste from landfills and reduces the demand for virgin plasticsmade from fossil-based resources, which consequently reduces greenhousegas emissions. In developed regions, such as the United States and theEuropean Union, rates of plastics recycling are increasing due togreater awareness by consumers, businesses, and industrial manufacturingoperations. The majority of recycled materials, including plastics, aremixed into a single stream which is collected and processed by amaterial recovery facility (MRF). At the MRF, materials are sorted,washed, and packaged for resale. Plastics can be sorted into individualmaterials, such as high-density polyethylene (HDPE), poly(ethyleneterephthalate) (PET), or mixed streams of other common plastics, such aspolypropylene (PP), low-density polyethylene (LDPE), poly(vinylchloride) (PVC), polystyrene (PS), polycarbonate (PC), and polyamides(PA). The single or mixed streams can then be further sorted, washed,and reprocessed into pellets that are suitable for re-use in plasticsprocessing, for example blow and injection molding.

Though recycled plastics are sorted into predominately uniform streamsand are washed with aqueous and/or caustic solutions, the finalreprocessed pellets often remain highly contaminated with unwanted wasteimpurities, such as spoiled food residue and residual perfumecomponents. In addition, recycled plastic pellets, except for those fromrecycled beverage containers, are darkly colored due to the mixture ofdyes and pigments commonly used to color plastic articles. While thereare some applications that are insensitive to color and contamination(for example, black plastic paint containers and concealed automotivecomponents), the majority of applications require non-colored pellets.The need for high quality, “virgin-like” recycled resin, is especiallyimportant for food and drug contact applications, such as foodpackaging. In addition to being contaminated with impurities and mixedcolorants, many recycled resin products are often heterogeneous inchemical composition and may contain a significant amount of polymericcontamination, such as recycled polypropylene contamination inpolyethylene and vice versa.

Mechanical recycling is the process of converting recycled plastic wasteinto a re-usable form for subsequent manufacturing. A more detailedreview of mechanical recycling and other plastics recovery processes aredescribed in Al-Salem, S. M., et al., Waste Management, 29(10) (2009),2625-2643. While advances in mechanical recycling technology haveimproved the quality of recycled polymers to some degree, there arefundamental limitations of mechanical decontamination approaches, suchas the physical entrapment of pigments within a polymer matrix. Thus,even with the improvements in mechanical recycling technology, the darkcolor and high levels of chemical contamination in currently availablerecycled plastic waste prevents broader usage of recycled resins by theplastics industry.

To overcome the fundamental limitations of mechanical recycling, therehave been many methods developed to purify contaminated polymers, suchas chemical recycling and solvent-based recycling. The latter methodsuse solvents to decontaminate and purify polymers. The use of solventsenables the extraction of impurities and the dissolution of polymers,which further enables alternative separation technologies. U.S. Pat. No.7,935,736 discloses a method for recycling polyester from a waste streamusing a solvent to dissolve the polyester prior to cleaning. The patentalso describes the need to use a precipitant to recover the polyesterfrom the solvent.

U.S. Pat. No. 6,555,588 discloses a method to produce a polypropyleneblend from a plastic mixture comprising other polymers. The patentdescribes the extraction of contaminants from a polymer at a temperaturebelow the dissolution temperature of the polymer in the selectedsolvent, such as hexane, for a specified residence period. The patentfurther describes increasing the temperature of the solvent (or adding asecond solvent) to dissolve the polymer prior to filtration.Furthermore, the patent describes the use of shearing or flow toprecipitate polypropylene from solution. The polypropylene blenddescribed in the patent contained polyethylene contamination up to 5.6wt %.

European Patent Application No. 849,312 discloses a process to obtainpurified polyolefins from a polyolefin-containing plastic mixture or apolyolefin-containing waste. The patent application describes theextraction of polyolefin mixtures or wastes with a hydrocarbon fractionof gasoline or diesel fuel with a boiling point above 90° C. attemperatures between 90° C. and the boiling point of the hydrocarbonsolvent. The patent application further describes contacting a hotpolyolefin solution with bleaching clay and/or activated carbon toremove foreign components from the solution. Furthermore, the patentapplication describes cooling the solution to temperatures below 70° C.to crystallize the polyolefin and then removing the solvent by a varietyof methods, such as heating the polyolefin above its melting point,evaporating the solvent in a vacuum, passing a gas stream through thepolyolefin precipitate, or extraction of the solvent with an alcohol orketone that boils below the melting point of the polyolefin.

U.S. Pat. No. 5,198,471 discloses a method for separating polymers froma physically commingled solid mixture (for example, waste plastics)containing a plurality of polymers using a solvent at a first lowertemperature to form a first single phase solution and a remaining solidcomponent. The patent further describes heating the solvent to highertemperatures to dissolve additional polymers that were not solubilizedat the first lower temperature, and the filtration of insoluble polymercomponents.

U.S. Pat. No. 5,233,021 discloses a method of extracting pure polymericcomponents from a multi-component structure (for example, waste carpets)by dissolving each component at an appropriate temperature and pressurein a supercritical fluid and then varying the temperature and/orpressure to extract particular components in sequence. However, similarto the '471 patent, the '021 patent only discloses filtration ofundissolved components.

U.S. Pat. No. 5,739,270 discloses a method and apparatus forcontinuously separating a polymer component of a plastic fromcontaminants and other components of the plastic using a co-solvent anda working fluid. The co-solvent at least partially dissolves the polymerand the second fluid (that is in a liquid, critical, or supercriticalstate) solubilizes components from the polymer and precipitates some ofthe dissolved polymer from the co-solvent. The patent further disclosesthe step of filtering the thermoplastic-co-solvent (with or without theworking fluid) to remove particulate contaminants, such as glassparticles.

The known solvent-based methods to purify contaminated polymers, asdescribed above, do not produce polymer with virgin-like opticalproperties. In the previous methods, co-dissolution and thus crosscontamination of other polymers often occurs. If an adsorbent is used, afiltration and/or centrifugation step is often employed to remove theused adsorbent from solution. In addition, isolation processes to removesolvent, such as heating, vacuum evaporation, and/or precipitation usinga precipitating chemical, are used to produce a polymer free of residualsolvent.

Accordingly, there is a need for a purification technology that can befed with contaminated polyethylene waste and produce polyethylene thathas “virgin-like” optical properties using simple and few unitoperations, and employing a solvent that is readily and economicallyavailable.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method for purifyingcontaminated reclaimed polyethylene (crPE) to produce recycledpolyethylene with virgin-like optical properties (vlPE) is presented.The method comprises: a) Obtaining said crPE; wherein said crPE isselected from the group consisting of post-consumer recycled (PCR)polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Obtaining a solvent; wherein said solvent andsaid crPE form a one-phase solution at a temperature and at a pressurehigher than the cloud point pressure corresponding to said temperature;wherein said cloud point pressure: (i) corresponds to a solution of saidcrPE in said solvent at about 5 wt % concentration; (ii) is amonotonically increasing function of temperature; (iii) exceeds thefollowing pressure levels: about 700 psig (48.3 barg) at about 120° C.,about 1,150 psig (79.3 barg) at about 140° C., about 1,450 psig (100barg) at about 160° C., and about 1,800 psig (124.1 barg) at about 180°C.; (iv) includes smooth extrapolations at temperatures lower than about120° C. and higher than about 180° C.; and (v) includes smoothinterpolations at temperatures between about 120° C. and about 180° C.;c) Extracting said crPE with said solvent at an extraction massconcentration of at least about 1 wt %, at an extraction temperature,and at an extraction pressure; wherein said extraction temperature isfrom about 120° C. to about 260° C.; wherein said extraction pressure isbelow the cloud point pressure corresponding to said extractiontemperature; and wherein an extracted contaminated reclaimedpolyethylene (ecrPE) is produced; d) Dissolving the ecrPE in saidsolvent at a dissolution mass concentration of at least about 1 wt %, ata dissolution temperature, and at a dissolution pressure; wherein saiddissolution temperature is from about 120° C. to about 260° C.; whereinsaid dissolution pressure is above the cloud point pressurecorresponding to said dissolution temperature; and wherein a firstsuspension comprising dissolved polyethylene (PE) and suspendedparticulate contaminants is produced; e) Settling said first suspensionat a settling temperature and at a settling pressure; wherein saidsettling temperature is from about 120° C. to about 260° C.; whereinsaid settling pressure is above the cloud point pressure correspondingto said settling temperature; and wherein a second suspension comprisingdissolved PE and suspended remaining particulate contaminants isproduced; 0 Purifying said second suspension at a purificationtemperature and at a purification pressure by contacting said secondsuspension with solid media; wherein said purification temperature isfrom about 120° C. to about 260° C.; wherein said purification pressureis above the cloud point pressure corresponding to said purificationtemperature; and wherein a third suspension comprising purer PE isproduced; and g) Separating said purer PE from said third suspension;and wherein said purer PE is said vlPE.

In another embodiment of the present invention, a method for purifyingcrPE to produce vlPE is presented. The method comprises: a) Obtainingsaid crPE; wherein said crPE is selected from the group consisting ofpost-consumer recycled (PCR) polyethylene, post-industrial recycled(PIR) polyethylene, and combinations thereof; b) Extracting said crPEwith n-pentane at an extraction mass concentration of about 3.5 wt %, atan extraction temperature of about 205° C., and at an extractionpressure of about 1,900 psig (131 barg) to produce an ecrPE; c)Dissolving the ecrPE in n-pentane at a mass concentration of about 3.5wt %, at a dissolution temperature of about 140° C., and at adissolution pressure of about 1,900 psig (131 barg) to produce a firstsuspension comprising dissolved polyethylene (PE) and suspendedparticulate contaminants; d) Settling said first suspension at about140° C. and at about 1,900 psig (131 barg) to produce a secondsuspension comprising dissolved PE and suspended remaining particulatecontaminants; e) Purifying said second suspension by contacting saidsecond suspension with solid media at about 140° C. and at about 1,900psig (131 barg) to produce a third suspension comprising purer PE;wherein said purification comprises contacting said second suspensionwith said solid media in a candle filter followed by an axial flowfilter; and wherein said solid media of said candle filter comprisediatomaceous earth and said solid media of said axial flow filtercomprise activated alumina; and f) Separating said purer PE from saidthird suspension; wherein said purer PE is said vlPE; and wherein saidvlPE has L* greater than about 82, a* greater than about −3, b* lessthan about 5, and Y less than about 40%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of cloud point pressure curves of solutions of HDPEin n-butane, n-pentane, and hexanes. The vapor pressure curves of the 3solvents are also included. Each solution contains about 5 wt % ofFormolene® HB5502F HDPE (Formosa Plastics Corp., Livingston, N.J.),which is a blow molding grade and has a melt flow index (MFI) of about0.35 g/10 min.

FIG. 2 is a block flow diagram showing the major components of theextraction step of the method of the present invention.

FIG. 3 is a block flow diagram showing the major components of thedissolution step of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

As used herein, the term “reclaimed polyethylene” refers to apolyethylene that was used for a previous purpose and then collected forthe purpose of recycling.

As used herein, the term “contaminated reclaimed polyethylene” (crPE)refers to a reclaimed polyethylene that was contaminated withparticulate contaminants and other contaminants. Non-limiting examplesof other contaminants are odors, flavors, dyes, surfactants, surfaceprints, etc.

As used herein, the term “recycled polyethylene” refers to a product ofa recycling process that has been fed with reclaimed polyethylene.

As used herein, the term “post-consumer recycled” (PCR) material refersto a material in a waste stream that an end consumer has used anddisposed of.

As used herein, the term “post-industrial recycled” (PIR) materialrefers to a material in a waste stream of a manufacturing plant that isproduced after the manufacture of a good or product. Non-limitingexamples of PIR materials are manufacturing wastes, such as industrialscrap and part trimmings.

As used herein, the term “solvent” refers to a material that dissolvespolyethylene and may also be at, near, or above its critical temperatureand critical pressure (critical point). It is well known to those havingordinary skill in the art that substances above their critical point areknown as “supercritical fluids” which do not have the typical physicalproperties (i.e., density) of a liquid.

As used herein, the term “dissolved” refers to the partial (at aminimum) incorporation of a polyethylene solute in a solvent at themolecular level.

As used herein, the term “standard boiling point” refers to the boilingtemperature at an absolute pressure of exactly 100 kPa (1 bar, 14.5psia, 0.9869 atm) as established by the International Union of Pure andApplied Chemistry (IUPAC).

As used herein, the term “suspension” refers to a suspension ofparticulate contaminants in a polyethylene solution.

As used herein, the term “particulate contaminants” refers toparticulate matter that is present throughout the bulk or surface ofpolyethylene articles. These particulate contaminants can be additivesthat suppliers typically incorporate into polyethylene to protect and/orextend its life, contaminants left onto the polyethylene articles fromtheir consumer use, contaminants attached to the polyethylene articlesduring their disposal in the waste stream and reclaiming, etc.Non-limiting examples of particulate contaminants, that suppliersincorporate into polyethylene, are antioxidants (either primary orsecondary), anti-blocking agents, anti-stat agents, UV stabilizers,flame retardants, and colorants.

As used herein, the term “solid media” refers to media, in particulate,woven, or non-woven shapes, used in filtration operations. Theseoperations can be axial flow or radial flow, or other operations.

As used herein, the term “purer polyethylene” refers to a polyethylenehaving fewer contaminants relative to the same polyethylene prior to apurification step.

As used herein, the term “extraction” refers to the process step oftransferring solute species from a liquid phase (or solid matrix) andacross a phase boundary to a separate immiscible liquid phase.

As used herein, the term “extracted” refers to a material having fewersolute species relative to the same material prior to an extractionstep.

As used here, the term “extracted reclaimed polyethylene” refers to areclaimed polyethylene having fewer solute species relative to the samereclaimed polyethylene prior to an extraction step.

As used herein, the term “virgin-like” material means a material thathas essentially similar properties and composition to a virgin material.

As used herein, the term “virgin-like optical properties” refers to L*(CIE (Commission Internationale de l'Eclairage) lightness axis; 0 isblack and 100 is white) greater than about 82, a* (CIE red-green axis;negative value is green, positive value is red, and 0 is neutral)greater than about −3, b* (CIE blue-yellow axis; negative value is blue,positive value is yellow, and 0 is neutral) lower than about 5, and Y(CIE contrast ratio opacity) lower than about 40%.

As used herein, the term “hexanes” refers to a blend of hexane isomers,such as normal hexane (at least 45 vol %, and typically, about 53 vol%), iso hexane (2-methylpentane, 3-methylpentane, and2,3-dimethylbutane), and neo hexane (2,2-dimethylbutane).

II. Feedstock—Waste Polyethylene

Unexpectedly, it has been found that solvents which form solutions ofwaste polyethylene and have a cloud point pressure that exceeds athreshold pressure at a certain temperature generate purer polyethylenewith virgin-like optical properties. Under these conditions, thesesolvents are typically considered poor solvents for polyethylene. On theother hand, solvents which form solutions of waste polyethylene and havea cloud point pressure that is lower than a threshold pressure at acertain temperature cannot generate purer polyethylene with virgin-likeoptical properties. Under these conditions, these solvents areconsidered θ or good solvents.

For polyethylene, non-limiting examples of poor solvents are normalbutane (n-butane) and normal pentane (n-pentane), and non-limitingexamples of θ or good solvents are normal hexane (n-hexane) and hexanes.For example, at 160° C., the cloud point pressure of a solution of about5 wt % polyethylene in n-pentane (poor solvent) is about 1,950 psig(134.4 barg) and that in n-butane (poor solvent) is about 4,550 psig(313.7 barg). In another example, at 160° C., the cloud point pressureof a solution of about 5 wt % polyethylene in hexanes (θ or goodsolvent) is about 380 psig (26.2 barg). As the number of carbon atoms inan alkane solvent increases, the alkane becomes a better solvent (e.g.,moves from poor to θ and then to good solvent).

Not wishing to be bound by any theory, applicants believe that key tothe conversion of waste polyethylene to purer polyethylene withvirgin-like optical properties is the quality of the solvent. If thesolvent is a poor solvent, then the polyethylene molecules are collapsedinto dense coils (like spheres, with solvent molecules essentiallyexcluded from these coils). The radius of gyration, R_(g), of thesedense coils is on the order of a few nm for a 100,000 Da polyethylenemolecule, and the expectation is that these dense coils do not interactwith the suspended particulate contaminants. If the solvent is a θsolvent, then the polyethylene molecules are expanded to some degreeassuming random walk conformation and include solvent molecules amongstthem. The R_(g) of these expanded molecules is about one order ofmagnitude higher than that of the dense coils in the poor solvent andabout a few hundreds of nm for a 100,000 Da polyethylene molecule. Also,the expectation is that some of these expanded polymer molecules areadsorbed onto the surface of the suspended particulate contaminants andthus inhibit their removal by the filtration media. Finally, if thesolvent is a good solvent, then the polyethylene molecules are ratherexpanded assuming self-avoiding walk conformation and include a lot ofsolvent molecules amongst them. The R_(g) is about one order ofmagnitude higher than that of the molecules in the θ solvent and about athousand nm for a 100,000 Da polyethylene molecule. Also, theexpectation is that some of these polyethylene molecules are adsorbedonto the surface of the suspended particulate contaminants and thusinhibit their removal by the filtration media.

The feedstock in the present invention is a contaminated reclaimedpolyethylene (crPE). In one embodiment of the present invention, amethod for purifying crPE to produce recycled polyethylene withvirgin-like optical properties (vlPE) comprises obtaining said crPE. Inanother embodiment of the present invention, the crPE is selected fromthe group consisting of post-consumer recycled (PCR) polyethylene,post-industrial recycled (PIR) polyethylene, special waste streampolyethylene, and combinations thereof. In yet another embodiment of thepresent invention, the crPE is selected from the group consisting of PCRpolyethylene, PIR polyethylene, and combinations thereof. In oneembodiment of the present invention, a method for purifying crPE toproduce vlPE comprises obtaining said crPE, wherein said crPE isselected from the group consisting of PCR polyethylene, PIRpolyethylene, and combinations thereof.

Non-limiting examples of sources of PCR polyethylene are curbsiderecycle streams (where end-consumers place used polymers from packagesand products into a designated bin for collection by a waste hauler orrecycler) and in-store “take-back” programs (where the consumer bringswaste polymers into a store and places the waste polymers in adesignated collection bin). A non-limiting example of sources of PIRpolyethylene is waste polymer streams produced during the manufacture orshipment of a good or product that are collected as unusable material bythe manufacturer (i.e., trim scraps, out of specification material, andstart-up scrap). Non-limiting examples of sources of special wastestream polyethylene are recycling of electronic waste (also known ase-waste); recycling of automobiles; and recycling of used carpeting andtextiles.

For the purposes of the present invention, the crPE is a homogenouscomposition of an individual polyethylene or a mixture of severaldifferent polyethylene compositions. Non-limiting examples ofpolyethylene compositions are homopolymers and copolymers of ethylene,such as HDPE, LDPE, LLDPE, copolymers of ethylene and alpha-olefins, andother polyethylene polymers that may be apparent to those havingordinary skill in the art.

Non-limiting examples of contamination in crPE are pigments, dyes,process aids, stabilizing additives (e.g., antioxidants), fillers, flameretardants, and other performance additives that were added to thepolyethylene during polymerization or conversion of the originalpolyethylene to the final form of an article and are necessary formarketing, branding, processability, and/or end use performance.Non-limiting examples of pigments are organic pigments, such as copperphthalocyanine; inorganic pigments, such as titanium dioxide; and otherpigments that may be apparent to those having ordinary skill in the art.A non-limiting example of an organic dye is Basic Yellow 51.Non-limiting examples of process aids are antistatic agents, such asglycerol monostearate; and slip-promoting agents, such as erucamide. Anon-limiting example of an antioxidant isoctadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate (BASF'sIrganox® 1076). Non-limiting examples of fillers are calcium carbonate,talc, and glass fibers. The crPE may also contain odors, surface prints,paper labels, adhesives for labels, dirt, and volatile and non-volatileorganic compounds. In addition, contaminants may result from interactionwith products, e.g., polyethylene packaging materials that containcleaning mixtures (e.g. limonene, surfactants, etc.), food (e.g. variousorganics), etc. The contamination may be particulate (e.g. fillers,dirt, particulate pigments, etc.) or non-particulate (e.g. dyes, odors,surfactants, volatile organic compounds, etc.).

In one embodiment of the present invention, said crPE comprisescontaminated reclaimed high-density polyethylene (crHDPE). In anotherembodiment of the present invention, said crPE comprises contaminatedreclaimed low-density polyethylene (crLDPE). In yet another embodimentof the present invention, said crPE comprises contaminated reclaimedlinear low-density polyethylene (crLLDPE). In even yet anotherembodiment of the present invention, said crPE comprises a mixture ofcrLDPE and crLLDPE.

In one embodiment of the present invention, said crPE is contaminatedreclaimed high-density polyethylene (crHDPE). In another embodiment ofthe present invention, said crPE is contaminated reclaimed low-densitypolyethylene (crLDPE). In yet another embodiment of the presentinvention, said crPE is contaminated reclaimed linear low-densitypolyethylene (crLLDPE). In even yet another embodiment of the presentinvention, said crPE is a mixture of crLDPE and crLLDPE.

III. Solvent

Polyethylene solutions exhibit a cloud point curve, which is theirliquid-liquid equilibrium curve. A typical method to measure a cloudpoint curve is with the use of a view cell, as this is well known tothose skilled in the art. A solution of a certain amount of polyethylenein a solvent is prepared at a specified temperature and high pressurewhere the solution is in a one-phase regime. Then, under stirring, thetemperature is held constant and the pressure is lowered. At somepressure, called cloud point pressure, the solution becomes cloudy andit enters the two-phase regime, i.e., a heavy phase (also called theraffinate (RAF) phase, which contains high concentration of polyethylenein the solvent) and a light phase (also called the extract (EXTR) phase,which contains a very low concentration of polyethylene in the solvent).From the two-phase regime, if the pressure is increased then thetwo-phase system will become a clear solution (one-phase regime) as thepressure crosses the cloud point pressure at that temperature.

Typical examples of cloud point pressure curves are shown in FIG. 1 withsolutions of a virgin HDPE in n-butane, n-pentane, and hexanes at about5 wt % concentration. Other concentrations of HDPE in solvents orconcentrations of various polyethylene grades (such as, HDPE, LDPE, andLLDPE) in solvents could shift these cloud point curves shown in FIG. 1in the pressure/temperature space. For the purposes of the presentinvention, we consider a solution with about 5 wt % virgin HDPEFormolene® HB5502F in a solvent as the reference solution and 160° C.temperature as the reference temperature.

The solvent of the present invention produces a solution withpolyethylene at about 5 wt % concentration that has a cloud pointpressure exceeding a certain level. In one embodiment of the presentinvention, the cloud point pressure of a solution of polyethylene atabout 5 wt % concentration exceeds about 1,450 psig (100 barg) at about160° C. In another embodiment of the present invention, the cloud pointpressure of a solution of polyethylene at about 5 wt % concentrationexceeds about 1,950 psig (134.4 barg) at about 160° C. In yet anotherembodiment of the present invention, the cloud point pressure of asolution of polyethylene at about 5 wt % concentration exceeds about3,000 psig (206.8 barg) at about 160° C. In even yet another embodimentof the present invention, the cloud point pressure of a solution ofpolyethylene at about 5 wt % concentration exceeds about 4,550 psig(313.7 barg) at about 160° C.

In one embodiment of the present invention, the cloud point pressure ofa solution of polyethylene at about 5 wt % concentration is about 2,300psig (158.6 barg) at about 180° C. In another embodiment of the presentinvention, the cloud point pressure of a solution of polyethylene atabout 5 wt % concentration is about 1,950 psig (134.4 barg) at about160° C. In yet another embodiment of the present invention, the cloudpoint pressure of a solution of polyethylene at about 5 wt %concentration is about 1,650 psig (113.8 barg) at about 140° C. In evenyet another embodiment of the present invention, the cloud pointpressure of a solution of polyethylene at about 5 wt % concentration isabout 1,200 psig (82.7 barg) at about 120° C.

In one embodiment of the present invention, the cloud point pressure ofa solution of polyethylene at about 5 wt % concentration is about 4,550psig (313.7 barg) at about 160° C. In another embodiment of the presentinvention, the cloud point pressure of a solution of polyethylene atabout 5 wt % concentration is about 4,300 psig (296.5 barg) at about140° C. In yet another embodiment of the present invention, the cloudpoint pressure of a solution of polyethylene at about 5 wt %concentration is about 4,050 psig (279.2 barg) at about 120° C.

For polyethylene solutions, the cloud point pressure is a monotonicallyincreasing function of temperature in the range between about 120° C.and about 260° C. As it is well known to those skilled in the art, thecloud point pressure is a monotonically increasing function oftemperature if for temperature 1 less than temperature 2, then the cloudpoint pressure (at temperature 1) is less than the cloud point pressure(at temperature 2).

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises: a) Obtaining said crPE; wherein said crPE isselected from the group consisting of post-consumer recycled (PCR)polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; and b) Obtaining a solvent; wherein said solventand said crPE form a one-phase solution at a temperature and at apressure higher than the cloud point pressure corresponding to saidtemperature; wherein said cloud point pressure: (i) corresponds to asolution of said crPE in said solvent at about 5 wt % concentration;(ii) is a monotonically increasing function of temperature; (iii)exceeds the following pressure levels: about 700 psig (48.3 barg) atabout 120° C., about 1,150 psig (79.3 barg) at about 140° C., about1,450 psig (100 barg) at about 160° C., and about 1,800 psig (124.1barg) at about 180° C.; (iv) includes smooth extrapolations attemperatures lower than about 120° C. and higher than about 180° C.; and(v) includes smooth interpolations at temperatures between about 120° C.and about 180° C.

In another embodiment of the present invention, a method for purifyingcrPE to produce vlPE comprises: a) Obtaining said crPE; wherein saidcrPE is selected from the group consisting of post-consumer recycled(PCR) polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; and b) Obtaining a solvent; wherein said solventand said crPE form a one-phase solution at a temperature and at apressure higher than the cloud point pressure corresponding to saidtemperature; wherein said cloud point pressure: (i) corresponds to asolution of said crPE in said solvent at about 5 wt % concentration;(ii) is a monotonically increasing function of temperature; (iii)exceeds the following pressure levels: about 2,200 psig (151.7 barg) atabout 120° C., about 2,650 psig (182.7 barg) at about 140° C., about3,000 psig (206.8 barg) at about 160° C., and about 3,300 psig (227.5barg) at about 180° C.; (iv) includes smooth extrapolations attemperatures lower than about 120° C. and higher than about 180° C.; and(v) includes smooth interpolations at temperatures between about 120° C.and about 180° C.

In yet another embodiment of the present invention, a method forpurifying crPE to produce vlPE comprises: a) Obtaining said crPE;wherein said crPE is selected from the group consisting of post-consumerrecycled (PCR) polyethylene, post-industrial recycled (PIR)polyethylene, and combinations thereof and b) Obtaining a solvent;wherein said solvent and said crPE form a one-phase solution at atemperature and at a pressure higher than the cloud point pressurecorresponding to said temperature; wherein said cloud point pressure:(i) corresponds to a solution of said crPE in said solvent at about 5 wt% concentration; (ii) is a monotonically increasing function oftemperature; (iii) includes the following pressure levels: about 1,200psig (82.7 barg) at about 120° C., about 1,650 psig (113.8 barg) atabout 140° C., about 1,950 psig (134.4 barg) at about 160° C., and about2,300 psig (158.6 barg) at about 180° C.; (iv) includes smoothextrapolations at temperatures lower than about 120° C. and higher thanabout 180° C.; and (v) includes smooth interpolations at temperaturesbetween about 120° C. and about 180° C.

In even yet another embodiment of the present invention, a method forpurifying crPE to produce vlPE comprises: a) Obtaining said crPE;wherein said crPE is selected from the group consisting of post-consumerrecycled (PCR) polyethylene, post-industrial recycled (PIR)polyethylene, and combinations thereof and b) Obtaining a solvent;wherein said solvent and said crPE form a one-phase solution at atemperature and at a pressure higher than the cloud point pressurecorresponding to said temperature; wherein said cloud point pressure:(i) corresponds to a solution of said crPE in said solvent at about 5 wt% concentration; (ii) is a monotonically increasing function oftemperature; (iii) includes the following pressure levels: about 4,050psig (279.2 barg) at about 120° C., about 4,300 psig (296.5 barg) atabout 140° C., and about 4,550 psig (313.7 barg) at about 160° C.; (iv)includes smooth extrapolations at temperatures lower than about 120° C.and higher than about 160° C.; and (v) includes smooth interpolations attemperatures between about 120° C. and about 160° C.

The normal boiling points of some solvents are as follows: iso-butane:−11.7° C.; iso-butylene: −6.9° C.; 1-butene: −6.3° C.; n-butane: −1° C.;2-butene: 0.8-3.7° C.; neo-pentane: 9.5° C.; iso-pentane: 27.8° C.;1-pentene: 30° C.; n-pentane: 36.1° C.; 2-pentene: 36.3° C.; iso-hexane:60° C.; 1-hexene: 63.9° C.; n-hexane: 68° C.; and 2-hexene: 69.1° C. Inone embodiment of the present invention, the solvent has a normalboiling point less than about 50° C. In another embodiment of thepresent invention, the solvent has a normal boiling point less thanabout 40° C. In yet another embodiment of the present invention, thesolvent has a normal boiling point less than about 20° C. In even yetanother embodiment of the present invention, the solvent has a normalboiling point less than about 0° C.

In one embodiment of the present invention, the solvent comprisesn-pentane. In another embodiment of the present invention, the solventcomprises n-butane. In yet another embodiment of the present invention,the solvent is selected from the group consisting of 1-pentene,iso-pentane, neo-pentane, 2-butene, 1-butene, iso-butane, and mixturesthereof.

In one embodiment of the present invention, the solvent is n-pentane. Inanother embodiment of the present invention, the solvent is n-butane.

In one embodiment of the present invention, said solvent is n-pentaneand said crPE is crHDPE. In another embodiment of the present invention,said solvent is n-pentane and said crPE is crLDPE. In yet anotherembodiment of the present invention, said solvent is n-pentane and saidcrPE is crLLDPE. In even yet another embodiment of the presentinvention, said solvent is n-pentane and said crPE is a mixture ofcrLDPE and crLLDPE.

In one embodiment of the present invention, said solvent is n-butane andsaid crPE is crHDPE. In another embodiment of the present invention,said solvent in n-butane and said crPE is crLDPE. In yet anotherembodiment of the present invention, said solvent is n-butane and saidcrPE is crLLDPE. In even yet another embodiment of the presentinvention, said solvent is n-butane and said crPE is a mixture of crLDPEand crLLDPE.

In one embodiment of the present invention, said solvent comprisesn-pentane and said crPE comprises crHDPE. In another embodiment of thepresent invention, said solvent comprises n-pentane and said crPEcomprises crLDPE. In yet another embodiment of the present invention,said solvent comprises n-pentane and said crPE comprises crLLDPE. Ineven yet another embodiment of the present invention, said solventcomprises n-pentane and said crPE comprises a mixture of crLDPE andcrLLDPE.

In one embodiment of the present invention, said solvent comprisesn-butane and said crPE comprises crHDPE. In another embodiment of thepresent invention, said solvent comprises n-butane and said crPEcomprises crLDPE. In yet another embodiment of the present invention,said solvent comprises n-butane and said crPE comprises crLLDPE. In evenyet another embodiment of the present invention, said solvent comprisesn-butane and said crPE comprises a mixture of crLDPE and crLLDPE.

IV. Extraction Step

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises extracting said crPE with a solvent at anextraction mass concentration of at least about 1 wt %, at an extractiontemperature, and an extraction pressure; wherein said extractiontemperature is from about 120° C. to about 260° C.; wherein saidextraction pressure is below the cloud point pressure corresponding tosaid extraction temperature; and wherein an extracted contaminatedreclaimed polyethylene (ecrPE) is produced.

The extraction step takes place in the two-phase regime of thesolvent-polyethylene system, i.e., below the cloud point pressure at thespecified temperature. As disclosed above, in the two-phase regime,there are the heavy phase (RAF phase) and the light phase (EXTR phase).

Not wishing to be bound by any theory, applicants believe that theextractable contamination migrates from the polyethylene in the heavyphase to the solvent in the light phase due to favorable partitioncoefficient of the extractable contamination between the solvent andpolyethylene in the extracting step. Extractable contamination is partof the contamination of the waste polyethylene and it might includeresidual processing aids added to polyethylene, residual productformulations which contacted polyethylene (such as, perfumes andflavors), dyes, and any other extractable material that may have beenintentionally added or unintentionally became incorporated intopolyethylene during waste collection and subsequent accumulation withother waste materials.

Non-limiting examples of liquid-liquid extraction (LLE) equipment thatcan be used in this extracting step are extraction columns (e.g.,static, agitated, or pulsed), mixer—settlers, and centrifugalextractors. Examples of commercial equipment that can be used are Kühnicolumns, SCHEIBEL® columns, KARR® columns, rotating disc contractorcolumns, packed columns, sieve columns, etc.

In one embodiment of the present invention, the extracting step takesplace in a pressure vessel that may be configured in a way that allowsfor continuous extraction of the polyethylene with the solvent. Inanother embodiment of the present invention, the pressure vessel may bea continuous liquid-liquid extraction column where molten polyethyleneis pumped into one end of the extraction column and the solvent ispumped into the same (co-current extraction) or the opposite(counter-current extraction) end of the extraction column.

In one embodiment of the present invention, the solvent or the lightphase containing the extracted contamination is removed from theprocess. In another embodiment of the present invention, the solventcontaining the extracted contamination is purified, recovered, andrecycled for use in the extracting step or a different step in themethod. In yet another embodiment of the present invention, theextracting step is performed in a batch mode, wherein the crPE is fixedin a pressure vessel as a polymer phase and the solvent is continuouslypumped through the fixed polymer phase. The extracting time or theamount of solvent used will depend on the desired purity of the finalpurer polyethylene and the amount of extractable contamination in thestarting crPE. In even yet another embodiment of the present invention,the solvent containing the extracted contamination is contacted withsolid media in a separate step as described in the purification sectionbelow.

In one embodiment of the present invention, the extraction massconcentration is at least about 1 wt %. In another embodiment of thepresent invention, the extraction mass concentration is at least about 2wt %. In yet another embodiment of the present invention, the extractionmass concentration is at least about 3 wt %. In even yet anotherembodiment of the present invention, the extraction mass concentrationis at least about 5 wt %. In one embodiment of the present invention,the extraction mass concentration is at least about 10 wt %. For thepurposes of the present invention, the extraction mass concentration isthe concentration of crPE in the two-phase crPE-solvent system (i.e., inboth the heavy and light phases) in the extracting step.

In one embodiment of the present invention, the extraction temperatureis from about 120° C. to about 260° C. In another embodiment of thepresent invention, the extraction temperature is from about 140° C. toabout 240° C. In yet another embodiment of the present invention, theextraction temperature is from about 160° C. to about 220° C. In evenyet another embodiment of the present invention, the extractiontemperature is from about 180° C. to about 200° C.

In one embodiment of the present invention, the extraction temperatureis about 205° C. In another embodiment of the present invention, theextraction temperature is about 220° C. In yet another embodiment of thepresent invention, the extraction temperature is about 230° C. In evenyet another embodiment of the present invention, the extractiontemperature is about 240° C.

In one embodiment of the present invention, the extraction pressure isfrom about 700 psig (48.3 barg) to about 6,000 psig (413.7 barg). Inanother embodiment of the present invention, the extraction pressure isfrom about 1,500 psig (103.4 barg) to about 5,000 psig (344.7 barg). Inyet another embodiment of the present invention, the extraction pressureis from about 2,000 psig (137.9 barg) to about 4,000 psig (275.8 barg).

In one embodiment of the present invention, the extraction pressure isabout 1,500 psig (103.4 barg). In another embodiment of the presentinvention, the extraction pressure is about 1,900 psig (131 barg). Inyet another embodiment of the present invention, the extraction pressureis about 2,500 psig (172.4 barg). In even yet another embodiment of thepresent invention, the extraction pressure is about 4,500 psig (310.3barg).

In one embodiment of the present invention, the solvent is n-pentane,the crPE is crHDPE, the extraction temperature is about 205° C., and theextraction pressure is about 1,900 psig (131 barg). In anotherembodiment of the present invention, the solvent is n-pentane, the crPEis crHDPE, the extraction temperature is about 230° C., and theextraction pressure is about 1,900 psig (131 barg). In yet anotherembodiment of the present invention, the solvent is n-pentane, the crPEis crHDPE, the extraction temperature is about 240° C., and theextraction pressure is about 1,900 psig (131 barg). In even yet anotherembodiment of the present invention, the solvent is n-pentane, the crPEis crHDPE, the extraction temperature is about 260° C., and theextraction pressure is about 1,900 psig (131 barg).

In one embodiment of the present invention, the method for purifyingcrPE to produce vlPE comprises: a) Obtaining said crPE; wherein saidcrPE is selected from the group consisting of PCR polyethylene, PIRpolyethylene, and combinations thereof; and b) Extracting said crPE withn-pentane at an extraction mass concentration of about 3.5 wt %, at anextraction temperature of about 205° C., and at an extraction pressureof about 1,900 psig (131 barg) to produce an extracted contaminatedreclaimed polyethylene (ecrPE).

In one embodiment of the present invention, the solvent is n-butane, thecrPE is crHDPE, the extraction temperature is about 200° C., and theextraction pressure is about 4,500 psig (310.3 barg). In anotherembodiment of the present invention, the solvent is n-butane, the crPEis crHDPE, the extraction temperature is about 240° C., and theextraction pressure is about 4,500 psig (310.3 barg). In yet anotherembodiment of the present invention, the solvent is n-butane, the crPEis crHDPE, the extraction temperature is about 260° C., and theextraction pressure is about 4,500 psig (310.3 barg).

V. Dissolution Step

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises: a) Obtaining said crPE; wherein said crPE isselected from the group consisting of post-consumer recycled (PCR)polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Obtaining a solvent; wherein said solvent andsaid crPE form a one-phase solution at a temperature and at a pressurehigher than the cloud point pressure corresponding to said temperature;wherein said cloud point pressure: (i) corresponds to a solution of saidcrPE in said solvent at about 5 wt % concentration; (ii) is amonotonically increasing function of temperature; (iii) includes thefollowing pressure levels: about 1,200 psig (82.7 barg) at about 120°C., about 1,650 psig (113.8 barg) at about 140° C., about 1,950 psig(134.4 barg) at about 160° C., and about 2,300 psig (158.6 barg) at 180°C.; (iv) includes smooth extrapolations at temperatures lower than about120° C. and higher than about 180° C.; and (v) includes smoothinterpolations at temperatures between about 120° C. and about 180° C.;c) Extracting said crPE with said solvent at an extraction massconcentration of at least about 1 wt %, at an extraction temperature,and at an extraction pressure; wherein, said extraction temperature isfrom about 110° C. to about 260° C.; wherein said extraction pressure isbelow the cloud point pressure corresponding to said extractiontemperature; and wherein an extracted contaminated reclaimedpolyethylene (ecrPE) is produced; and d) Dissolving the ecrPE in saidsolvent at a dissolution mass concentration of at least about 1 wt %, ata dissolution temperature, and at a dissolution pressure; wherein saiddissolution temperature is from about 120° C. to about 260° C.; whereinsaid dissolution pressure is above the cloud point pressurecorresponding to said temperature; and wherein a first suspensioncomprising dissolved polyethylene (PE) and suspended particulatecontaminants is produced.

In another embodiment of the present invention, a method for purifyingcrPE to produce vlPE comprises: a) Obtaining said crPE; wherein saidcrPE is selected from the group consisting of post-consumer recycled(PCR) polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Extracting said crPE with n-pentane at anextraction mass concentration of about 3.5 wt %, at an extractiontemperature of about 205° C., and at an extraction pressure of about1,900 psig (131 barg) to produce an extracted contaminated reclaimedpolyethylene (ecrPE); and c) Dissolving the ecrPE in n-pentane at adissolution mass concentration of about 3.5 wt %, at a dissolutiontemperature of about 140° C., and a dissolution pressure of about 1,900psig (131 barg) to produce a first suspension comprising dissolvedpolyethylene (PE) and suspended particulate contaminants. In yet anotherembodiment of the present invention, the solvent is n-pentane, the crPEis crHDPE, the extraction temperature is about 205° C. and theextraction pressure is about 1,900 psig (131 barg), and the dissolutiontemperature is about 140° C. and the dissolution pressure is about 1,900psig (131 barg).

In the dissolution step, the ecrPE is brought into the one-phase regimeof the polyethylene-solvent system by changing the pressure and/ortemperature so that the dissolution pressure is higher than the cloudpoint pressure corresponding to the dissolution temperature. Thedissolution is aided with mixing at the dissolution temperature andpressure, that can be achieved in typical equipment, such as mixingcolumns and vessels, static systems, etc. Furthermore, the dissolutiontemperature and pressure can be controlled in such a way to enabledissolution of polyethylene while not dissolving other polymers orpolymer mixtures. This controllable dissolution enables the separationof polyethylene from polymer mixtures. Once the polyethylene isdissolved into the solvent in this dissolution step, the particulatecontaminants (e.g. pigments, fillers, dirt, etc.), which are part of thecrPE, will be released from the polyethylene and be suspended, thusforming a first suspension.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises: a) Extracting the crPE in a solvent at anextraction temperature and at an extraction pressure to produce anextracted crPE (ecrPE); and b) Dissolving the ecrPE in said solvent at adissolution temperature and at a dissolution pressure. In anotherembodiment of the present invention, a method for purifying crPE toproduce vlPE comprises: a) Extracting the crPE in n-pentane at anextraction temperature and at an extraction pressure to produce anextracted crPE (ecrPE); and b) Dissolving the ecrPE in n-pentane at adissolution temperature and at a dissolution pressure. In yet anotherembodiment of the present invention, a method for purifying crPE toproduce vlPE comprises: a) Extracting the crPE in n-pentane at anextraction temperature from about 120° C. and about 260° C., and at anextraction pressure below the cloud point pressure corresponding to saidextraction temperature to produce an extracted crPE (ecrPE); and b)Dissolving the ecrPE in n-pentane at a dissolution temperature fromabout 120° C. and about 260° C., and at a dissolution pressure above thecloud point pressure corresponding to said dissolution temperature. Ineven yet another embodiment of the present invention, a method forpurifying crPE to produce vlPE comprises: a) Extracting the crPE inn-pentane at an extraction temperature from about 140° C. and about 240°C., and at an extraction pressure below the cloud point pressurecorresponding to said extraction temperature to produce an extractedcrPE (ecrPE); and b) Dissolving the ecrPE in n-pentane at a dissolutiontemperature from about 120° C. to about 160° C., and at a dissolutionpressure above the cloud point pressure corresponding to saiddissolution temperature.

In one embodiment of the present invention, the dissolution temperatureis from about 120° C. to about 260° C. In another embodiment of thepresent invention, the dissolution temperature is from about 140° C. toabout 240° C. In yet another embodiment of the present invention, thedissolution temperature is from about 160° C. to about 220° C. In evenyet another embodiment of the present invention, the dissolutiontemperature is from about 180° C. to about 200° C.

In one embodiment of the present invention, the dissolution temperatureis about 120° C. In another embodiment of the present invention, thedissolution temperature is about 140° C. In yet another embodiment ofthe present invention, the dissolution temperature is about 160° C. Ineven yet another embodiment of the present invention, the dissolutiontemperature is about 180° C.

In one embodiment of the present invention, the dissolution pressure isfrom about 700 psig (48.3 barg) to about 6,000 psig (413.7 barg). Inanother embodiment of the present invention, the dissolution pressure isfrom about 1,500 psig (103.4 barg) to about 5,000 psig (344.7 barg). Inyet another embodiment of the present invention, the dissolutionpressure is from about 2,000 psig (137.9 barg) to about 4,000 psig(275.8 barg).

In one embodiment of the present invention, the dissolution pressure isabout 1,500 psig (103.4 barg). In another embodiment of the presentinvention, the dissolution pressure is about 1,900 psig (131 barg). Inyet another embodiment of the present invention, the dissolutionpressure is about 2,500 psig (172.4 barg). In even yet anotherembodiment of the present invention, the dissolution pressure is about4,500 psig (310.3 barg).

In one embodiment of the present invention, the dissolution massconcentration is at least about 1 wt %. In another embodiment of thepresent invention, the dissolution mass concentration is at least about2 wt %. In yet another embodiment of the present invention, thedissolution mass concentration is at least about 3 wt %. In even yetanother embodiment of the present invention, the dissolution massconcentration is at least about 5 wt %. In one embodiment of the presentinvention, the dissolution mass concentration is at least about 10 wt %.

In one embodiment of the present invention, the dissolution solvent isthe same as the extraction solvent. In another embodiment of the presentinvention, the dissolution solvent is different than the extractionsolvent. In one embodiment of the present invention, the dissolutionsolvent is n-butane, and the extraction solvent is n-pentane.

After the dissolution is achieved and the first suspension is formed,the suspended contaminants are settled (in the settling operation) byexperiencing a force that uniformly moves them in the direction of theforce. Typically, the applied settling force is gravity, but can also bea centrifugal, centripetal, or other force. The amount of applied forceand duration of the settling operation (settling time) will depend uponseveral parameters, including, but not limited to, particle size of thecontaminant particles, contaminant particle density, density of thesolution, and viscosity of the solution. Some of the key parameters thatdetermine the solution viscosity are the chemical composition of thesolvent, the molecular weight and concentration of the polyethylenedissolved in the solvent, and the temperature and pressure of thesolution. At the end of the settling operation, a layer of settledparticulate contaminants and a second suspension are produced. Thesecond suspension includes the suspended remaining particulatecontaminants, that have not been settled in the settled layer.Typically, the larger contaminant particles are settled, and the smallercontaminant particles are suspended in the second suspension. Typically,the temperature, pressure, and concentration conditions of the settlingoperation are the same as those of the dissolution step. Processing aidsto help the settling operation, such as flocculation aids, can also beadded in the first suspension or in the contaminated reclaimed PE or atany point in this method.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises settling said first suspension at a settlingtemperature and at a settling pressure; said settling temperature isfrom about 120° C. to about 260° C.; said settling pressure is above thecloud point pressure corresponding to said settling temperature; and asecond suspension comprising dissolved PE and suspended remainingparticulate contaminants is produced. In another embodiment of thepresent invention, a method for purifying crPE to produce vlPE comprisessettling said first suspension at a settling temperature and at asettling pressure; said settling temperature is from about 140° C. toabout 240° C.; said settling pressure is above the cloud point pressurecorresponding to said settling temperature; and a second suspensioncomprising dissolved PE and suspended remaining particulate contaminantsis produced. In yet another embodiment of the present invention, amethod for purifying crPE to produce vlPE comprises settling said firstsuspension at a settling temperature and at a settling pressure; saidsettling temperature is from about 160° C. to about 220° C.; saidsettling pressure is above the cloud point pressure corresponding tosaid settling temperature; and a second suspension comprising dissolvedPE and suspended remaining particulate contaminants is produced. In evenyet another embodiment of the present invention, a method for purifyingcrPE to produce vlPE comprises settling said first suspension at asettling temperature and at a settling pressure; said settlingtemperature is from about 180° C. to about 200° C.; said settlingpressure is above the cloud point pressure corresponding to saidsettling temperature; and a second suspension comprising dissolved PEand suspended remaining particulate contaminants is produced.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises settling said first suspension at about 140°C. and about 1,900 psig (131 barg) to produce a second suspensioncomprising dissolved PE and suspended remaining particulatecontaminants. In another embodiment of the present invention, thesolvent is n-pentane, the crPE is crHDPE, the extraction temperature isabout 205° C. and the extraction pressure is about 1,900 psig (131barg), the dissolution temperature is about 140° C. and the dissolutionpressure is about 1,900 psig (131 barg), and the settling temperature isabout 140° C. and the settling pressure is about 1,900 psig (131 barg).

The purification of said second suspension proceeds by contacting saidsecond suspension with solid media. For the purposes of the presentinvention, the solid media are any solid materials that remove at leastsome of the contamination (particulate or not) from the secondsuspension. Although not wishing to be bound by any theory, applicantsbelieve that the solid media remove the contamination by a variety ofmechanisms. Non-limiting examples of possible mechanisms includeadsorption, absorption, size exclusion, ion exclusion, ion exchange, andother mechanisms that are well known to those having ordinary skill inthe art. Furthermore, the pigments and other contaminants commonly foundin crPE may be polar compounds and may preferentially interact with thesolid media, which may also be at least slightly polar. The polar-polarinteractions are especially favorable when a non-polar solvent, such asalkane, is used as the solvent.

In one embodiment of the present invention, the solid media are selectedfrom the group consisting of inorganic material, carbon-based material,and mixtures thereof. Non-limiting examples of inorganic materials aresilica (silicon oxide), alumina (aluminum oxide), activated alumina(activated aluminum oxide), iron oxide, aluminum silicate, magnesiumsilicate, amorphous volcanic glass, reclaimed glass, silica gel,diatomaceous earth, sand, quartz, perlite, fuller's earth, bentonite,and mixtures thereof. In another embodiment of the present invention,the inorganic material is selected from the group consisting of silica,alumina, iron oxide, aluminum silicate, amorphous volcanic glass, andmixtures thereof. In yet another embodiment of the present invention,the inorganic material comprises diatomaceous earth. In even yet anotherembodiment of the present invention, the inorganic material comprisesactivated alumina. In one embodiment of the present invention, theinorganic material comprises reclaimed glass.

Non-limiting examples of carbon-based materials are anthracite coal,carbon black, coke, activated carbon, cellulose, and mixtures thereof.In one embodiment of the present invention, the carbon-based material isselected from the group consisting of anthracite coal, carbon black,coke, activated carbon, cellulose, and mixtures thereof. In anotherembodiment of the present invention, the carbon-based material comprisesactivated carbon.

In one embodiment of the present invention, the solid media arecontacted with the second suspension in a mixing vessel for a specifiedamount of time while the contents of the vessel are mixed. In anotherembodiment of the present invention, the solid media are removed fromthe mixing vessel via a solid-liquid separation step. Non-limitingexamples of solid-liquid separation steps include filtration,decantation, centrifugation, and settling.

In one embodiment of the present invention, the second suspension ispassed through a stationary bed of solid media. In another embodiment ofthe present invention, the solid media are placed in an axial flowfilter. In yet another embodiment of the present invention, the solidmedia are placed in a radial flow filter. A non-limiting example of aradial flow filter is a candle filter. In even yet another embodiment ofthe present invention, the solid media are placed in a candle filter.

In one embodiment of the present invention, the height or length of thestationary bed of solid media is greater than 5 cm. In anotherembodiment of the present invention, the height or length of thestationary bed of solid media is greater than 10 cm. In yet anotherembodiment of the present invention, the height or length of thestationary bed of solid media is greater than 20 cm. In even yet anotherembodiment of the present invention, the solid media are replaced asneeded to maintain a desired purity of polyethylene. In one embodiment,the solid media are regenerated and re-used in the purification step. Inanother embodiment, the solid media are regenerated by fluidizing thesolid media during a backwashing step.

In one embodiment of the present invention, the purification comprisescontacting the second suspension with the solid media in a candle filterfollowed by an axial flow filter, and the solid media of the candlefilter comprise diatomaceous earth and the solid media of the axial flowfilter comprise activated alumina.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises: a) Obtaining said crPE; wherein said crPE isselected from the group consisting of post-consumer recycled (PCR)polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Obtaining a solvent; wherein said solvent andsaid crPE form a one-phase solution at a temperature and at a pressurehigher than the cloud point pressure corresponding to said temperature;wherein said cloud point pressure: (i) corresponds to a solution of saidcrPE in said solvent at about 5 wt % concentration; (ii) is amonotonically increasing function of temperature; (iii) includes thefollowing pressure levels: about 1,200 psig (82.7 barg) at about 120°C., about 1,650 psig (113.8 barg) at about 140° C., about 1,950 psig(134.4 barg) at about 160° C., and about 2,300 psig (158.6 barg) atabout 180° C.; (iv) includes smooth extrapolations at temperatures lowerthan about 120° C. and higher than about 180° C.; and (v) includessmooth interpolations at temperatures between about 120° C. and about180° C.; c) Extracting said crPE with said solvent at an extraction massconcentration of at least about 1 wt %, at an extraction temperature,and an extraction pressure; wherein said extraction temperature is fromabout 120° C. to about 260° C.; wherein said extraction pressure isbelow the cloud point pressure corresponding to said extractiontemperature; and wherein an extracted contaminated reclaimedpolyethylene (ecrPE) is produced; d) Dissolving the ecrPE in saidsolvent at a dissolution mass concentration of at least about 1 wt %, ata dissolution temperature, and at a dissolution pressure; wherein saiddissolution temperature is from about 120° C. to about 260° C.; whereinsaid dissolution pressure is above the cloud point pressurecorresponding to said dissolution temperature; and wherein a firstsuspension comprising dissolved polyethylene (PE) and suspendedparticulate contaminants is produced; e) Settling said first suspensionat a settling temperature and at a settling pressure; wherein saidsettling temperature is from about 120° C. to about 260° C.; whereinsaid settling pressure is above the cloud point pressure correspondingto said settling temperature; and wherein a second suspension comprisingdissolved PE and suspended remaining particulate contaminants isproduced; and f) Purifying said second suspension at a purificationtemperature and at a purification pressure by contacting said secondsuspension with solid media; wherein said purification temperature isfrom about 120° C. to about 260° C.; wherein said purification pressureis above the cloud point pressure corresponding to said purificationtemperature; and wherein a third suspension comprising purer PE isproduced.

In another embodiment of the present invention, a method for purifyingcrPE to produce vlPE comprises: a) Obtaining said crPE; wherein saidcrPE is selected from the group consisting of post-consumer recycled(PCR) polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Extracting said crPE with n-pentane at anextraction mass concentration of about 3.5 wt %, at an extractiontemperature of about 205° C., and at an extraction pressure of about1,900 psig (131 barg) to produce an extracted contaminated reclaimedpolyethylene (ecrPE); c) Dissolving the ecrPE in n-pentane at a massconcentration of about 3.5 wt %, at a dissolution temperature of about140° C., and at a dissolution pressure of about 1,900 psig (131 barg) toproduce a first suspension comprising dissolved polyethylene (PE) andsuspended particulate contaminants; e) Settling said first suspension atabout 140° C. and at about 1,900 psig (131 barg) to produce a secondsuspension comprising dissolved PE and suspended remaining particulatecontaminants; and f) Purifying said second suspension by contacting saidsecond suspension with solid media at about 140° C. and at about 1,900psig (131 barg) to produce a third suspension comprising purer PE;wherein said purification comprises contacting said second suspensionwith said solid media in a candle filter followed by an axial flowfilter; and wherein said solid media of said candle filter comprisediatomaceous earth and said solid media of said axial flow filtercomprise activated alumina.

In yet another embodiment of the present invention, the solvent isn-pentane; the crPE is crHDPE; the extraction temperature is about 205°C. and the extraction pressure is about 1,900 psig (131 barg); thedissolution temperature is about 140° C. and the dissolution pressure isabout 1,900 psig (131 barg); the settling temperature is about 140° C.and the settling pressure is about 1,900 psig (131 barg); and thepurification temperature is about 140° C. and the purification pressureis about 1,900 psig (131 barg).

Typically, the type of solvent and polyethylene mass concentration inthe purification step, and purification temperature and pressure are thesame as those in the dissolution step and/or those in the extractionstep.

In one embodiment of the present invention, the purification massconcentration is at least about 1 wt %. In another embodiment of thepresent invention, the purification mass concentration is at least about2 wt %. In yet another embodiment of the present invention, thepurification mass concentration is at least about 3 wt %. In even yetanother embodiment of the present invention, the purification massconcentration is at least about 5 wt %. In one embodiment of the presentinvention, the purification mass concentration is at least about 10 wt%.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises separating the purer PE from the thirdsuspension. In another embodiment of the present invention, theseparation of the purer PE from the third suspension takes place at aseparation temperature and at a separation pressure; and wherein the PEprecipitates from solution and is no longer dissolved in the solvent. Inyet another embodiment of the present invention, the separation of thepurer PE from the solvent is accomplished by reducing the separationpressure at a fixed separation temperature. In even yet anotherembodiment of the present invention, the separation of the purer PE fromthe solvent is accomplished by reducing the separation temperature at afixed separation pressure. In one embodiment of the present invention,the separation of the purer PE from the solvent is accomplished byincreasing the separation temperature at a fixed separation pressure. Inanother embodiment, the separation of the purer PE from the solvent isaccomplished by reducing both the separation temperature and separationpressure.

The solvent can be partially or completely converted from the liquid tothe vapor phase by controlling the separation temperature and separationpressure. In one embodiment of the present invention, the separation ofthe purer PE from the solvent is accomplished without completelyconverting the solvent into a 100% vapor by controlling the separationtemperature and separation pressure of the solvent during the separationstep.

The separation of the purer PE from the solvent can be accomplished byany method of liquid-liquid or liquid-solid separation. Non-limitingexamples of liquid-liquid or liquid-solid separations includefiltration, decantation, centrifugation, and settling.

VI Purer PE

In one embodiment of the present invention, the purer PE, which may besourced from PCR PE, is essentially contaminant-free, pigment-free,odor-free, homogenous, and similar in properties to virgin PE (vPE). Inanother embodiment of the present invention, the physical properties ofthe solvent may enable more energy efficient methods for separation ofthe solvent from the purer PE.

In one embodiment of the present invention, the purer PE has virgin-likeoptical properties (vlPE). In another embodiment of the presentinvention, the purer PE has virgin-like optical properties (vlPE); andthe vlPE has L* greater than about 82, a* greater than about −3, b* lessthan about 5, and Y less than about 40%.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises: a) Obtaining said crPE; wherein said crPE isselected from the group consisting of post-consumer recycled (PCR)polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Obtaining a solvent; wherein said solvent andsaid crPE form a one-phase solution at a temperature and at a pressurehigher than the cloud point pressure corresponding to said temperature;wherein said cloud point pressure: (i) corresponds to a solution of saidcrPE in said solvent at about 5 wt % concentration; (ii) is amonotonically increasing function of temperature; (iii) includes thefollowing pressure levels: about 1,200 psig (82.7 barg) at about 120°C., about 1,650 psig (113.8 barg) at about 140° C., about 1,950 psig(134.4 barg) at about 160° C., and about 2,300 psig (158.6 barg) atabout 180° C.; (iv) includes smooth extrapolations at temperatures lowerthan about 120° C. and higher than about 180° C.; and (v) includessmooth interpolations at temperatures between about 120° C. and about180° C.; c) Extracting said crPE with said solvent at an extraction massconcentration of at least about 1 wt %, at an extraction temperature,and an extraction pressure; wherein said extraction temperature is fromabout 120° C. to about 260° C.; wherein said extraction pressure isbelow the cloud point pressure corresponding to said extractiontemperature; and wherein an extracted contaminated reclaimedpolyethylene (ecrPE) is produced; d) Dissolving the ecrPE in saidsolvent at a dissolution mass concentration of at least about 1 wt %, ata dissolution temperature, and at a dissolution pressure; wherein saiddissolution temperature is from about 120° C. to about 260° C.; whereinsaid dissolution pressure is above the cloud point pressurecorresponding to said dissolution temperature; and wherein a firstsuspension comprising dissolved polyethylene (PE) and suspendedparticulate contaminants is produced; e) Settling said first suspensionat a settling temperature and at a settling pressure; wherein saidsettling temperature is from about 120° C. to about 260° C.; whereinsaid settling pressure is above the cloud point pressure correspondingto said settling temperature; and wherein a second suspension comprisingdissolved PE and suspended remaining particulate contaminants isproduced; 0 Purifying said second suspension at a purificationtemperature and at a purification pressure by contacting said secondsuspension with solid media; wherein said purification temperature isfrom about 120° C. to about 260° C.; wherein said purification pressureis above the cloud point pressure corresponding to said purificationtemperature; and wherein a third suspension comprising purer PE isproduced; and g) Separating said purer PE from said third suspension;and wherein said purer PE is said vlPE.

In another embodiment of the present invention, a method for purifyingcrPE to produce vlPE comprises: a) Obtaining said crPE; wherein saidcrPE is selected from the group consisting of post-consumer recycled(PCR) polyethylene, post-industrial recycled (PIR) polyethylene, andcombinations thereof; b) Extracting said crPE with n-pentane at anextraction mass concentration of about 3.5 wt %, at an extractiontemperature of about 205° C., and at an extraction pressure of about1,900 psig (131 barg) to produce an extracted contaminated reclaimedpolyethylene (ecrPE); c) Dissolving the ecrPE in n-pentane at a massconcentration of about 3.5 wt %, at a dissolution temperature of about140° C., and at a dissolution pressure of about 1,900 psig (131 barg) toproduce a first suspension comprising dissolved polyethylene (PE) andsuspended particulate contaminants; d) Settling said first suspension atabout 140° C. and at about 1,900 psig (131 barg) to produce a secondsuspension comprising dissolved PE and suspended remaining particulatecontaminants; e) Purifying said second suspension by contacting saidsecond suspension with solid media at about 140° C. and at about 1,900psig (131 barg) to produce a third suspension comprising purer PE;wherein said purification comprises contacting said second suspensionwith said solid media in a candle filter followed by an axial flowfilter; and wherein said solid media of said candle filter comprisediatomaceous earth and said solid media of said axial flow filtercomprise activated alumina; and f) Separating said purer PE from saidthird suspension; wherein said purer PE is said vlPE; and wherein saidvlPE has L* greater than about 82, a* greater than about −3, b* lessthan about 5, and Y less than about 40%.

In yet another embodiment of the present invention, the solvent isn-pentane; the crPE is crHDPE; the extraction temperature is about 205°C. and the extraction pressure is about 1,900 psig (131 barg); thedissolution temperature is about 140° C. and the dissolution pressure isabout 1,900 psig (131 barg); the settling temperature is about 140° C.and the settling pressure is about 1,900 psig (131 barg); thepurification temperature is about 140° C. and the purification pressureis about 1,900 psig (131 barg); and the vlPE has L* greater than about82, a* greater than about −3, b* less than about 5, and Y less thanabout 40%.

In one embodiment of the present invention, a method for purifying crPEto produce vlPE comprises de-inking of said crPE. A non-limiting exampleof a de-inking process is described in U.S. Pat. No. 9,616,595, whichdiscloses an ink removal step with the use of an aqueous cleaning fluidwith high pH and selective cleaning agents, such as dodecyl sulfate, andhigh turbulence.

VII Examples Example 1—Comparative

A sample of post-consumer recycled HDPE “mixed color” flake (also calledHDPE Jazz Flake or HDPE JF; used to produce the TPS-8000 product; TABBPackaging Solutions, LLC; Canton, Mich.) was processed using theexperimental apparatuses shown in FIGS. 2 and 3 and the followingprocedure (at Phasex Corporation, 125 Flagship Drive, North Andover,Mass.). 75 g of HDPE JF were loaded into a 7.695 L (working volume)autoclave (Model 4552M; Parr Instrument Company; Moline, Ill.) equippedwith an overhead mechanical stirrer. The air from the autoclaveheadspace was removed with 3 repeat cycles of vacuuming and N₂ purging.The autoclave was then filled with 3,472 g of hexanes (Catalog #:35900ACS; >98.5% Hexane isomers and methyl cyclopentane; Pharmco byGreenfield Global, Inc.; Brookfield, Conn.) and its contents wereequilibrated at an internal temperature of about 230° C. and pressure ofabout 600 psig (41.4 barg), i.e., extraction conditions. At thoseextraction conditions the material in the autoclave is in a two-phaseregime, i.e., one phase with hexanes and a small amount oflow-molecular-weight HDPE JF dissolved (light or extract phase) and theother phase with a large amount of HDPE JF dissolved in hexanes (heavyor raffinate phase). The autoclave material was then extracted 5 timesusing the experimental configuration of FIG. 2 and the followingprocedure: the autoclave material was stirred for about 10 min at about680 rpms, then it was allowed to settle for about 10 min, and finallyone vessel volume of hexanes was flushed through the autoclave into theextract collection flask through an expansion valve. The aboveextraction procedure was repeated four more times. The materialcollected from all 5 extraction cycles was labeled “PE-27 Fraction 1”.The remaining autoclave material was then dissolved in hexanes at thedissolution conditions of about 210° C. and about 1900 psig (131 barg),thus creating a one-phase system. The dissolved material was purifiedand collected using the experimental configuration of FIG. 3 and thefollowing procedure: the autoclave material was stirred for about 60 minat about 680 rpms, then it was allowed to settle for about 60 min, thenthe autoclave material was removed from the autoclave by opening theautoclave valve and allowing it to pass through a candle filter, anactivated alumina column, an expansion valve, and get collected into theproduct collection flask. The candle filter (FUNDABAC® Filter Highpressure TSD with filter volume about 1 L; Dr Mueller AG, Maennedorf,Switzerland) had a stainless-steel sock/hose (about 5.5 in. (14 cm)long) coated with about 18 g of diatomaceous earth (Celatom® FW-40; EPMinerals, LLC; Reno, Nev.). The activated alumina column had about 0.68in. (1.73 cm) ID and about 30 in. (76.2 cm) length, and it was chargedwith about 120 g of spherical activated alumina particles 1/16 in. (1.59mm), 7×14 mesh (1.41 mm-2.83 mm; Catalog #: 87014; Sorbent Technologies,Inc.; Norcross, Ga.). The product fractions were labelled sequentiallystarting with “PE-27 Fraction 2”. Fractions were collected until”.Fractions were collected until a low solubility was noticed/calculated.After all samples were collected, the autoclave was equilibrated toatmospheric pressure and room temperature. All residual material in theautoclave was then collected as a residuum sample.

The PE-27 Fraction 2, PE-27 Fraction 3, and PE-27 Fraction 4 werecompression molded into 1-mm thick and 30×30 mm windows (following theprinciples of ASTM D4703-16 “Standard Practice for Compression MoldingThermoplastic Materials into Test Specimens, Plaques, or Sheets”). Thetemperature used for the compression molding was about 160° C., thepressure was about 1.8 metric tons, and Teflon sheets were used asrelease liners. The optical properties of these windows were thenmeasured (following the principles of ASTM E308 “Standard Practice forComputing the Colors of Objects by Using the CIE System”) using theLabScan XE (Hunter Associates Laboratory, Inc.; Reston, Va.) and D65/10conditions, i.e., D65 light source and 10-degree observer angle. Theresults were: L*=77.4±1.4; a*=−5.3±1.5; b*=10.7±2.2; and Y(opacity)=78.2%±14.1%.

For comparison, a typical blow-molding virgin HDPE (Formolene® HB5502F;Formosa Plastics Corp.; Livingston, N.J.) has the following opticalvalues: L*=85.9±0.1; a*=−1.3±0.0; b*=−0.3±0.0; and Y(opacity)=41.3%±0.6%. Also, a typical film grade virgin low-density PE(LDPE) (Dow™ 640i; Dow Chemical Company, Midland, Mich.) has thefollowing optical values: L*=83.7±0.2; a*=−0.5±0.0; b*=1.3±0.1; and Y(opacity)=17.8%±1.5%. Finally, a typical film grade virgin linearlow-density PE (LLDPE) (Dowlex™ 2045G; Dow Chemical Company; Midland,Mich.) has the following optical values: L*=82.6±1.2; a*=−1.0±0.1;b*=2.1±0.2; and Y (opacity)=15.4%±1.9%. The relatively low value of b*for the virgin HDPE resin vs. that for the LDPE and LLDPE resins is dueto specific additives used for HDPE.

For comparison, the HDPE JF, which was fed into EXAMPLE 1, in pelletform, had the following optical properties: L*=64.6±3.6; a*=16±13;b*=16.8±6.4; and Y (opacity)=100%. A natural recycled HDPE material(KWR101-150; KW Plastics, Inc.; Troy, Ala.) had the following opticalproperties: L*=77.2±0.7; a*=−0.8±0.3; b*=5.7±0.2; and Y(opacity)=57.2%±1.6%.

Example 2

The feed of EXAMPLE 1 was processed the same way as in EXAMPLE 1;however, the solvent was n-pentane (3,200 g were charged in theautoclave at the beginning of the experiment; and the cloud point curveof the HDPE solution in n-pentane at about 5 wt % concentration is shownin FIG. 1 ), extraction conditions were 205° C. and 1900 psig (131barg), and dissolution conditions were 140° C. and 1900 psig (131 barg).The product fractions were labelled sequentially starting with “PE-30Fraction 2”. The optical properties of the product fractions were:L*=83.8±0.6; a*=−2.4±0.3; b*=3.5±0.4; and Y (opacity)=34.0%±4.7%.

The results from EXAMPLES 1 and 2, virgin polyethylene samples, HDPE JF,and natural recycled HDPE are summarized in TABLE 1 below.

TABLE 1 EXAMPLE # L*, [—] a*, [—] b*, [—] Y, [%] Virgin HDPE 85.9 ± 0.1−1.3 ± 0.0 −0.3 ± 0.0  41.3 ± 0.6 (HB5502F) HDPE Jazz Flake 64.6 ± 3.6 16.0 ± 12.8 16.8 ± 6.4  100 TPS-8000 KWR101-150 77.2 ± 0.7 −0.8 ± 0.35.7 ± 0.2 57.2 ± 1.6 Natural rHDPE Virgin LDPE 83.7 ± 0.2 −0.5 ± 0.0 1.3± 0.1 17.8 ± 1.5 (640i) Virgin LLDPE 82.6 ± 1.2 −1.0 ± 0.1 2.1 ± 0.215.4 ± 1.9 (2045G) 1 (comparative) 77.4 ± 1.4 −5.3 ± 1.5 10.7 ± 2.2  78.2 ± 14.1 2 (inventive) 83.8 ± 0.6 −2.4 ± 0.3 3.5 ± 0.4 34.0 ± 4.7

The foregoing description is given for clearness of understanding only,and no unnecessary limitations should be understood therefrom, asmodifications within the scope of the invention may be apparent to thosehaving ordinary skill in the art.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, comprising any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A method for purifying contaminated reclaimedpolyethylene (crPE) to produce recycled polyethylene with virgin-likeoptical properties (vlPE) comprising: a. Obtaining said crPE; whereinsaid crPE is selected from the group consisting of post-consumerrecycled (PCR) polyethylene, post-industrial recycled (PIR)polyethylene, and combinations thereof; b. Obtaining an extractionsolvent; wherein said extraction solvent and said crPE form a one-phasesolution at a temperature and at a pressure higher than the cloud pointpressure corresponding to said temperature; wherein said cloud pointpressure: i. corresponds to a solution of said crPE in said extractionsolvent at about 5 wt % concentration; ii. is a monotonically increasingfunction of temperature; iii. exceeds the following pressure levels:about 700 psig (48.3 barg) at about 120° C., about 1,150 psig (79.3barg) at about 140° C., about 1,450 psig (100 barg) at about 160° C.,and about 1,800 psig (124.1 barg) at about 180° C.; iv. includes smoothextrapolations at temperatures lower than about 120° C. and higher thanabout 180° C.; and v. includes smooth interpolations at temperaturesbetween about 120° C. and about 180° C.; c. Extracting said crPE withsaid extraction solvent at an extraction mass concentration of at leastabout 1 wt %, at an extraction temperature, and an extraction pressure;wherein said extraction temperature is from about 120° C. to about 260°C.; wherein said extraction pressure is below the cloud point pressurecorresponding to said extraction temperature; and wherein an extractedcontaminated reclaimed polyethylene (ecrPE) is produced; d. Dissolvingthe ecrPE in a dissolution solvent at a dissolution mass concentrationof at least about 1 wt %, at a dissolution temperature, and at adissolution pressure; wherein said dissolution temperature is from about120° C. to about 260° C.; wherein said dissolution pressure is above thecloud point pressure corresponding to said dissolution temperature; andwherein a first suspension comprising dissolved polyethylene (PE) andsuspended particulate contaminants is produced; e. Settling said firstsuspension at a settling temperature and at a settling pressure; whereinsaid settling temperature is from about 120° C. to about 260° C.;wherein said settling pressure is above the cloud point pressurecorresponding to said settling temperature; and wherein a secondsuspension comprising dissolved PE and suspended remaining particulatecontaminants is produced; f. Purifying said second suspension at apurification temperature and at a purification pressure by contactingsaid second suspension with solid media; wherein said purificationtemperature is from about 120° C. to about 260° C.; wherein saidpurification pressure is above the cloud point pressure corresponding tosaid purification temperature; and wherein a third suspension comprisingpurer PE is produced; and g. Separating said purer PE from said thirdsuspension; and wherein said purer PE is said vlPE; wherein said vlPEhas an L* greater than about 82, a* greater than about −3, b* lower thanabout 5, and Y lower than about 40%.
 2. The method of claim 1, whereinsaid cloud point pressure is about 1,200 psig (82.7 barg) at about 120°C., about 1,650 psig (113.8 barg) at about 140° C., about 1,950 psig(134.4 barg) at about 160° C., and about 2,300 psig (158.6 barg) atabout 180° C.
 3. The method of claim 1, wherein said dissolution solventis n-butane and said extraction solvent is n-pentane.
 4. The method ofclaim 1, wherein said dissolution solvent is the same as said extractionsolvent.
 5. The method of claim 4, wherein said extraction solvent isn-butane.
 6. The method of claim 4, wherein said extraction solvent isn-pentane.
 7. The method of claim 1, wherein said crPE comprisescontaminated reclaimed high-density polyethylene (crHDPE).
 8. The methodof claim 1, wherein said crPE comprises contaminated reclaimedlow-density polyethylene (crLDPE).
 9. The method of claim 1, whereinsaid crPE comprises contaminated reclaimed linear low-densitypolyethylene (crLLDPE).
 10. The method of claim 1, wherein said crPEcomprises a mixture of crLDPE and crLLDPE.
 11. The method of claim 6,wherein said crPE is crHDPE.
 12. The method of claim 1, wherein saidextraction mass concentration is greater than about 2 wt %.
 13. Themethod of claim 12, wherein said extraction mass concentration isgreater than about 5 wt %.
 14. The method of claim 1, wherein said solidmedia are selected from the group consisting of inorganic material,carbon-based material, and mixtures thereof.
 15. The method of claim 14,wherein said inorganic material is selected from the group consisting ofsilica, alumina, iron oxide, aluminum silicate, amorphous volcanicglass, and mixtures thereof.
 16. The method of claim 15, wherein saidinorganic material comprises activated alumina.
 17. The method of claim14, wherein said carbon-based material is selected from the groupconsisting of anthracite coal, carbon black, coke, activated carbon,cellulose, and mixtures thereof.
 18. The method of claim 1, wherein saidsolid media are placed in an axial flow filter.
 19. The method of claim1, wherein said solid media are placed in a candle filter.
 20. Themethod of claim 1, wherein said purification comprises contacting saidsecond suspension with said solid media in a candle filter followed byan axial flow filter; and wherein said solid media of said candle filtercomprise diatomaceous earth and said solid media of said axial flowfilter comprise activated alumina.
 21. The method of claim 2, whereinsaid extraction solvent is n-pentane; wherein said crPE is crHDPE;wherein said extraction temperature is about 205° C. and said extractionpressure is about 1,900 psig (131 barg); wherein said dissolutiontemperature is about 140° C. and said dissolution pressure is about1,900 psig (131 barg); wherein said settling temperature is about 140°C. and said settling pressure is about 1,900 psig (131 barg); whereinsaid purification temperature is about 140° C. and said purificationpressure is about 1,900 psig (131 barg); and wherein said vlPE has L*greater than about 82, a* greater than about −3, b* less than about 5,and Y less than about 40%.